(loosely) A contradiction in terms. Historically, an oxymoron was a paradox with a point, where the contradiction seems absurd at first glance, and yet is deliberate, its purpose being to underscore a point or to draw attention to a concealed point.
By far the most massive planet in our solar system, Jupiter features giant hurricanes, auroras, abstract artistic cloudswirls, and maybe even a solid core. It also protects Earth by gravitationally clearing the solar system of asteroids and comets.
Jupiter is the largest planet in our Solar System. One Thousand Earths would find in the volume of Jupiter. Had it been a few dozen times bigger, its core would have produced nuclear thermal reactions and it would have shone by its own light. Jupiter is a Star which failed. Mostly composed of Hydrogen, Helium, some other stuff too.